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Protection Circuits
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
Need of Protection
• A thyristor may be subjected to
– High di/dt
– High dv/dt
– Over voltages
Need of Protection
– Over voltages
– Over currents
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
di/dt protection
• Thyristor is a gate controlled device & turned on by gate pulse
• When Thyristor turns on, there is a transition of the charge carriers all the way through its junction junction
• Local hot spot: Due to large rate of rise of anode current (di/dt) than the spreading of charge carriers, localized heat generation will take place. This is called as Local hot spot.
• Typical di /dt limit value:20-500 A/µ sec.
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
dv/dt protection
• In the forward blocking state of the Thyristor, junction J1 & junction J3 are forward biased & only junction J2 is reverse biased.
• Junction J2 work as a capacitor with constant • Junction J2 work as a capacitor with constant capacitance, Cj (junction capacitance).
• If dva/dt increases, leakage current through the J2 junction increases.
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
• Due to this leakage current, the devise will be turned On in absence of Gate pulse; this is dv/dt triggering.
dv/dt protection
• Typical values of dv/dt : 20-500 V/µsec.
• The use of the snubber circuit which can be connetced in parallel with the Thyristor, can prevent this false turn-on by dv/dt change.
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
Snubber Circuit
Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
Working of Snubber Circuit
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
Working of Snubber Circuit
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
Types of Overvoltage :
- Internal Over voltages
- During commutation of thyristor (power devices).
Over Voltage Protection
- External Over voltages
- Due to interruption of current in inductive circuits.
- dv / dt
- Due to Lightning stroke on source feeders.
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
Overvoltage Protection Circuits :
1. Snubber Circuit
- For the protection of dv/d t rating.
- Design of snubber circuit.
Over Voltage Protection
- Design of snubber circuit.
2. Using Comparators
- To cut-off either supply voltage or load.
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
Overcurrent Causes :
1. Overcurrent due to faults
2. Overcurrent due to short circuit
3. Overcurrent due to surge current
Over Current Protection
3. Overcurrent due to surge current
4. Overcurrent due to rise in junction temperature
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
Over current Protection Circuits :
1. Using Semiconductor Fuse
2. di/dt protection
Over Current ProtectionOver Current Protection
- By designing a proper reactor in series with device
3. Using electronic Crowbar protection circuit
4. Using Current Transformer and Comparators
- To cut-off either supply voltage or load.
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
Gate Protection
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
• Losses during working of power devices:
i) On-state loss
ii) Switching loss (during turn on & turn off)
iii) Losses due to leakage current
Cooling & Heat Sinks
iii) Losses due to leakage current
iv) Gate drive loss
• A large amount of heat is generated due to these losses
• To maintain the devise temperature in a particular
range, cooling must be used to transfer this heat from
device to atmosphere.International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057
Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
- A heat sink is a passive heat exchanger that cools a device by dissipating heat into the surrounding medium like air / water / etc.
- Heat sinks are used with high-power
Cooling & Heat Sinks
- Heat sinks are used with high-power semiconductor devices where the heat dissipation ability of the basic device is insufficient to moderate its temp.
- A heat sink is designed to maximize its surface area in contact with the cooling medium surrounding it.
International Institute of Information Technology, I²IT, P-14 Rajiv Gandhi Infotech Park, Hinjawadi, Pune - 411 057 Tel - +91 20 22933441 / 2 / 3 | Website - www.isquareit.edu.in ; Email - info@isquareit.edu.in
For further details please contact
Prof. Varsha Degaonkar
THANK YOU!!
Prof. Varsha Degaonkar
varshad@isquareit.edu.in
Department of Electronics & Telecommunication
International Institute of Information Technology
I²IT
Hinjawadi, Pune
www.isquareit.edu.in
Ph. - +91 20 22933441
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